This application relates to optical polarization of light and polarization-mode dispersion in optical media, and more specifically, to techniques and systems for emulating and compensating polarization-mode dispersion in optical media such as optical fibers.
Various optical media are birefringent by exhibiting different refractive indices for different polarizations of light. Fibers, for example, may be birefringent and the axis of birefringence of a fiber may change with time, often randomly with the fluctuations in the operating conditions such as stresses or temperatures. Accordingly, the polarization of an optical signal, which may be represented by two polarization components along two orthogonal principal polarization states, can vary and thus be significantly distorted after propagation. This effect is called polarization-mode dispersion (“PMD”) and the first-order of PMD may be characterized by the average differential group delay (“DGD”) between the two principal states of polarization.
In general, effects of this polarization-mode dispersion are undesirable in various applications including optical fiber communication systems. Hence, it is desirable to characterize PMD effects and provide means to mitigate the PMD effects. One way of characterizing PMD effects is to use a PMD emulator to emulate actual PMD in a system of interest, such as a fiber system. For example, such a PMD emulator may be used to test a PMD compensator prior to actual deployment of the compensator.